MythBusters did a short segment regarding light bulbs.
Lights On or Off
Myth: You save on energy bills by leaving lights on. Some people believe
that the energy to turn on lights exceeds savings of turning lights off.
They talked to Mark Reisfelt, manager of the Independent Electric Supply
where they purchased their light bulbs. He felt that it was best to turn
the lights off.
To test the myth, they needed to measure energy usage during startup,
maintenance (steady state), and shutdown.
For steady state energy consumption, they turned on several different
types of bulbs for 60 minutes and measured their consumption using a
Kill A Watt: * Incandescent 90 Wh * Compact Fluorescent (CFL): 10 Wh *
Halogen: 70 Wh * Metal halide 60 Wh * LED: 1 Wh * Fluorescent: 10 Wh
For startup energy consumption, Grant hooked up an inductive current
loop to a computer and measured the amount of energy used when the
turned on the bulbs. With an inductive current loop, you run a wire
through the center, which induces a current in the loop. This current is
then measured by a digital sampling oscilloscope.
Based on the amount of energy consumed turning on the bulb, they were
able calculated how long the bulb would have to be turned off in order
to make it worth the energy savings, i.e. "It's best to turn off the
bulb if you are leaving the room for":
* Incandescent: 0.36 seconds
* CFL: 0.015 seconds
* Halogen: .51 seconds
* LED: 1.28 seconds
* Fluorescent: 23.3 seconds
In other words, its almost always best to turn the bulb off. Even the 23
seconds for the fluorescent lights isn't very long, and the rest of the
times are pretty much blinks of an eye. Bulb Longevity
They tested one final element of this myth: frequently turning lights on
and off decreases their life span, thus leading to greater costs. Grant
setup a timer and relay to turn the bulbs on and off repeatedly every 2
minutes. After six weeks, only the LED bulb was still working. Based on
this test, they extrapolated that it would take five years of ordinary
usage to cause the bulbs to burn out.
* busted *
Side-note: 105-year bulb
Grant and Kari visited the Livermore/Pleasanton Fire Department to view
their light bulb that has been burning for 105 years. It has a carbon
filament that is much thicker than modern bulbs and also burns much
cooler/darker. You can check on the light using the bulb's webcam.
The 23.3 seconds is more than the actual truth for fluorescents.
Fluorescent fixtures that draw increased current during starting also have
their power factor reduced during starting, and the above setup appears to
me to measure only current consumption.
- Don Klipstein ( email@example.com)
Fluorescents and HID lamps (such as metal halide) do suffer wear from
starting. Halogen and HID lamps can also age badly if they spend a lot of
"on time" incompletely warmed up.
2 weeks being on half the time is 504 hours. Many incandescents are
only rated to have average life expectancy of 750 hours.
I have seen the webcam picture. Based on this and web searching, I
suspect teh filament is indeed running at an unusually low temperature,
and with much less energy efficiency than that of modern incandescents.
You can get 230V lightbulbs. Some electrical/lighting supply places, as
well as online outfits such as bulbs.com, sell them. At 120V, they should
easily last a century. A 200W 230V lightbulb at 120V consumes about 75
watts, and produces about 2/3 the light output of better 40 watt 120V
incandescents. A "century bulb" is easy to achieve, but no bargain.
- Don Klipstein ( firstname.lastname@example.org)
It could be that what I am seeing isnt a direct failure of the LED but there
are 12 traffic signals from my house to work and 4 of them have sections
that are out or flcikering and these lights are only about a year old. Of
course this could represent the failure of only few LEDS in a few thousand
as I imagine the LEDS are probably arrange in series /paralell clusters
where if oneLED failed several others would also be taken out.
There's stray wire running from the 440 up at the telephone pole down to his
light socket. Funny how nobody has noticed it before.
Seriously, the primary causes of short incadescent light bulb lifespan are
1) too much voltage (an AC voltmeter can check this)
2) too much heat
3) too much vibration (unfrosted bulbs can handle heat and
vibration better as they run cooler)
4) poor quality light bulbs.
A floating neutral causes enough other -- and more dramatic and widespread --
symptoms that, in the absence of those other symptoms, it does not merit
consideration when the only observed symptom is short bulb life in a *single*
Doug Miller (alphageek at milmac dot com)
While I have seen such a circuit more than once, especially with
freezers, where owners want to make sure the power is still on, I did not
indicate both the lamp and the frig on the same circuit, but rather paired
on opposite legs of two circuits sharing a neutral. My answer would also
apply if many other items were on that same circuit pair, but if the other
devices were not sensitive to voltage swings or were not high amp users.
I find Joseph's idea entirely reasonable. His original post was "say
with" - an illustration. There are lots of possibilities of 2 circuits
with loose common neutral. Like 2 general purpose circuits with a light
on one and a heater on the other. Doesn't have to be only a light on one
circuit, just that the light be all that is on, or as Joseph wrote, all
that is sensitive.
If the unbalanced load of one circuit is going thru the lamp and
burning it out, where is it going when the light is off?
You should have lights and appliances. When the appliances are off
where is it going?
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